Isomerization of olefins with thioacetic acid



3,071,364 Patented Jan. 1, 1963 3,071,364 ISOMEMZATION F OLEFINS WITHTHIOACETIC ACID William J. Bailey, University Park, Md. University ofMaryland, College Park, Md.) N0 Drawing. Filed Apr. 4, 1960, Ser. No.19,501 Claims. (Cl. 260-666) The present invention is concerned with theisomerization of olefins, particularly of internal olefins to terminalolefins.

An object of this invention is to provide a new and novel process forthe isomerization of olefins. A particular object is to provide a methodfor the conversion of internal olefins to terminal olefins. These andfurther objects of the invention will be evident as the discussionproceeds.

It has now been found that olefins can be converted into isomers thereofwith the unsaturation' in a different position by reacting them withthioacids and then subjecting the reaction mixture to pyrolysis torelease the desired olefin. The unsymmetrically substituted olefins,especially internal olefins, are preferred starting materials. The loweralkyl thioacids, especially thioacetic acid, are preferred thioacids.Additionally, the olefin and thioacid are reacted at temperaturespreferably between about 20 to 50 C. and the resulting product subjectedto pyrolysis at temperatures preferably between about 450 to 550 C. Aparticularly preferred embodiment of this invention comprises thereaction of 2-methyl-2-butene with thioacetic acid at 0 to 50 C. andthen subjecting the reaction mixture to pyrolysis at 450 to 550 C. toobtain B-methyIbutene-l. These and other embodiments of the inventionwill be evident from the discussion hereinafter.

The present invention will be more readily understood from the followingexamples.

Example I Z-methyl-Z-butene was mixed with thioacetic acid controllingthe temperature at essentially room temperature. The reaction wasessentially instantaneous and the yield obtained was 82 percent. Thenthe reaction mixture was passed through a hot tube maintained at 520 C.to efiect pyrolysis. The yield of olefin product thus obtained was 83percent which consisted of 59 percent 3-methylbutene-1 and 41 percent ofZ-methyl-Z-butene.

Example 11 Employing the procedure of Example I, l-methylcyclohexene-lwas reacted with thioacetic acid and a 93 percent yield of predominantlythe cis isomer was obtained. The resulting mixture was then passedthrough the hot tube again maintained at 520 C. in which manner a 77percent yield of olefin product was obtained of which 80 percent was3-methylcyclohexene-l and 20 percent was l-methyl-l-cyclohexene.

The above examples are presented by way of illustration and otherexamples -will now be evident to those skilled in the art.

As illustrated by the above examples, the olefins employed arepreferably unsymmetrically substituted olefins, especially internalolefins. Generally, such olefins will contain up to and including 30carbon atoms. Typical examples of such olefins includeZ-methyI-Z-butene, 2- methyl-Z-pentene, 2-methyl 2hexene,3-methyl-2-hexene, 2-methyl-2-octene, Z-methyl octadecene-Z,l-methylcyclohexene-l, l-ethylcyclohexene-l, and the like. Thus, whenthese or other unsymmetrically substituted olefins are substituted inthe above examples, similar results are obtained.

The acids which are employed in the process of this invention are thethioacids. Included in this definition are also th dithioacids. Thus,such compounds are organic compounds in which divalent sulfur hasreplaced some or all of the oxygen atoms of the carboxyl group. Typicalexamples of such thioacids include thioacetic acid, thiopropionic acid,thiobutyric acid, thiobenzoic acid, dithioacetic acid, and the like. Ingeneral, such thioacids will contain up to about 18 carbon atoms in thehydrocarbon moieties. The alkyl thioacids in which the alkyl groupscontain up to and including about 8 carbon atoms are preferred.Accordingly, when the above and other thio and dithio acids aresubstituted in the above examples, equally satisfactory results areobtained.

The temperature at which the reaction of the thioacid with the olefin isconducted is generally between about 0 to C. For best results andpractical operation, it is desirable to maintain the temperature between20 and 50 C. This reaction is essentially instantaneous and externalcooling is employed, if necessary, to maintain the reaction temperature.The pyrolysis of the resulting non- Markownikofi addition product isconducted at temperatures sufiicient to effect the dissociation orpyrolysis and generally above about 350 C. For best results in order toavoid side reactions, it is preferable to conduct the pyrolysis betweenabout 450 to 550 C.

While the above discussion has been concerned primarily with thestep-wise addition reaction and subsequent pyrolysis, it is tobeunderstood that both operations can be conducted in one step by merelymixing the olefin and acid and then rapidly passing through a hot tubeor some suitable means to effect the pyrolysis in essentiallysimultaneous operations. Generally, however, it has been found moreadvantageous to employ the stepwise addition and pyrolysis operations.

Although such are not required, various organic solvents can beemployed, particularly to effect heat control of the addition reaction.For this purpose, the hydrocarbons, ethers, and amines, especiallytertiary amines, are well suited. Typical examples of the hydrocarbonsinclude the hexanes, octanes, nonanes, decanes, benzene, toluene, andthe like. Typical examples of the ethers include diethyl ether, dipropylether, dibutyl ether, diamyl ether, tetrahydrofuran, dioxane, and thepolyethers such as the dimethyl and diethyl ethers of ethylene glycol,diethylene glycol, triethylene glycol, and tetraethylene glycol. Ingeneral, such solvents are preferably inert in the reaction and liquidunder the addition reaction conditions. The aforementioned ethers,particularly the polyethers, are especially preferred organic solvents.Other examples of organic solvents which can be employed in the processof this invention will now be evident. Such solvents can be employed invarying amounts as between about 0.01 to 100 parts per part by weight ofthe olefin.

While not essential, advantage is achieved in faster reaction and higheryields when the process of this invention is conducted in the furtherpresence of free radical catalysts or light, such as ultra-violet light.The organic peroxides are particularly suitable free radical catalystsas, for example, benzoyl peroxide, lauroyl peroxide, stearoyl peroxide,acetyl peroxide, succinoyl peroxide, and the like. When employed, suchcan be present in minor amount as, for example, 0.001 part per part byweight of the olefin and up to about 0.1 and higher parts by Weight perpart by weight of the olefin.

The products produced according to the process of this invention are ofconsiderable utility. By way of example, the terminal olefins such as3-methylbutene-l and 4- methylpentene-l are admirably suited forpolymerization reactions to produce fibers. They can also be added todiborane, particularly in the aforementioned ethers, at room temperatureto produce the corresponding organoborane compounds. For example, whendiborane is reacted in. the dimethyl ether of diethylene glycol at roomtemperature with 3-methylbutene-1, tri(3-methylbutyl)- borane isobtained in good yield. The olefins can also be hydrated by knowntechniques to form the corresponding alcohols. Additionally, they can beoxidized to form the corresponding epoxides by known techniques. Theseand other uses of the products of this invention will now be evident.

Having thus described the process of this invention, it is not intendedthat it be limited except as set forth in the following claims.

I claim:

1. The process which comprises reacting an unsymmetrically substitutedinternal olefin with an organic thioacid and then pyrolyzing theresultant product to form an alpha isomer of said olefin wherein theunsaturation is non-adjacent to the substituted carbon atom.

2. A process for the production of 3-rnethylbutene-1 which comprisesreacting 2-methylbutene-2 with thioacetic acid and then subjecting theresulting product to pyrolysis at a temperature between about 450 to 550C.

3. The process of claim 2. wherein the reaction of 2- methyl butene-2and thioacetic acid is conducted at about room temperature.

4. The process of claim 2 wherein the reaction of 2- methyl butene-Z andthioacetic acid is conducted at about room temperature and thesubsequent pyrolysis is conducted at a temperature of about 520 C.

5. A process for the production of 3-rnethy1 cyclohexene-l whichcomprises reacting l-methyl cyclohexene-l with thioacetic acid and thensubjecting the resultant product to pyrolysis at a temperature of about520 C.

References Cited in the file of this patent UNITED STATES PATENTS2,128,971 Snow Sept. 6, 1938 2,425,858 Beach Aug. 19, 1947 OTHERREFERENCES Ipatiefl et al.: Journal of American Chemical Society, 1939,vol. 61, pages 71-74.

Advanced Organic Chemistry (Wheland), published by John Wiley & Sons,Inc., second ed., 1949, (pages 666 and 667 relied on. (Copy in Div.31.).

Advanced Organic Chemistry (Royals), published by Constable and Company,Ltd., 1956 (page 371 relied on). (Copy in Div. 31.)

1. THE PROCESS WHICH COMPRISES REACTING AN UNSYMMETRICALLY SUBSTITUTEDINTERNAL OLEFIN WITH AN ORGANIC THIOACID AND THEN PYROLYZING THERESULTANT PRODUCT TO FORM AN ALPHA ISOMER OF SAID OLEFIN WHEREIN THEUNSATURATION IS NON-ADJACENT TO THE SUBSTITUTED CARBON ATOM.